Refolding Mutant p53: A Strategy for Cancer Prevention in Li-Fraumeni Syndrome

PROJECT SUMMARY - PROJECT 1 Li-Fraumeni syndrome (LFS), an inherited disorder arising in heterozygous carriers of germline mutations in TP53, is associated with early-onset cancers in many different tissues of origin. Because TP53 has been studied so extensively, a unique opportunity exists to intervene early – prior to tumor formation – in LFS individuals. Whether germline or somatic, most cancer-associated TP53 mutations are missense mutations that disrupt p53’s ability to bind DNA. While some of these mutations map to residues in direct contact with DNA, many do not. Rather, these mutations reduce p53’s thermodynamic stability, so that an insufficient amount of (mutant) p53 is correctly folded: this leads to loss of function (LOF). Many of these mutations also confer oncogenic gain of function (GOF) activities. Among Li-Fraumeni individuals, evidence suggests that the earliest stages in the emergence of precancerous lesions, and progression of these lesions to cancer, derive from mutant p53’s GOF activities. Ongoing work in the Karanicolas lab focuses on developing drugs that bind and stabilize the folded conformation of mutant p53, to directly correct the missense defects that underlie the LOF and GOF activities. These “refolder drugs” are designed to bind a region on the protein surface that is separate from all of p53’s most common mutations, so that the same drug can be applied irrespective of the specific mutation. We have tested these drugs in diverse cancer cell lines harboring many different mutations in TP53. Through these studies, we have confirmed that these refolder drugs both: 1) restore LOF from mutant p53, and 2) revert mutant p53’s GOF activities. The objectives of our proposed project are three-fold. First, we will define the set of mutations characteristic of LFS individuals that can be addressed by this new class of agents. Second, we will optimize our current “best” agent to enhance its expected safety and efficacy in animal studies. Third, we will test the safety of the resulting agents’ in mice heterozygous for a TP53 mutation seen frequently in LFS individuals, and efficacy in a mouse model of p53-mediated squamous carcinoma that provides clear milestones of the progression from precancer to cancer. Successful completion of these studies will serve as important proof-of-concept that these p53 refolding agents hold the potential to become new drugs for prevention and early interception of cancer in LFS individuals.